Bone grafting is widely used to treat fractures and bone defect areas. Autogenous cancerous bone, which is taken from one site in the graftee and implanted in another site in the graftee, is currently the most effective bone graft and provides the scaffolding to support the distribution of the bone healing response and also provides the connective tissue progenitor cells which form new cartilage or bone. However, the harvest of autogenous bone results in significant cost and morbidity, including scars, blood loss, pain, prolonged operative and rehabilitation time and risk of infection. Furthermore, in some clinical settings, the volume of material necessary at the graft site can exceed the volume which can be extracted from the available autograft. Accordingly, alternatives to autografts have been developed in an attempt to reduce the problem of morbidity and cost of bone grafting procedures.
Several purified or synthetic materials, including ceramics, biopolymers, processed allograft bone and collagen-based matrices have been investigated or developed to serve as substitutes for autografts. The FDA has approved a porous coral derived synthetic hydroxyapatite ceramic for use in contained bone defects. A purified collagen/ceramic composite material is also approved for use in acute long bone fractures. Although these materials avoid the morbidity involved in harvesting autografts from the graftee and eliminate problems associated with a limited amount of available autograft, the clinical effectiveness of the synthetic materials generally is less than autografts.
Synthetic graft materials have also been used as carriers for bone marrow cells. When such composite materials have been implanted into skeletal defects, the connective tissue progenitor cells differentiated into skeletal tissue. In some instances, composite implants were made by soaking the synthetic graft material in a cell suspension obtained from bone marrow. However, the connective tissue progenitor cells, which have the capacity to differentiate into cartilage, bone and other connective tissue such as fat, muscle, and fibrous tissue are present in the bone marrow in very minute amounts. The numbers of such cells present in 1 ml of bone marrow varies widely from subject to subject ranging from about 100 cells to 20,000 cells depending to large extent on the age of the donor. This represents a mean of about one in 20,000 to one in 40,000 of the nucleated cells in bone marrow.
Demineralized bone material from allogenic sources has been available for over fifty years and has been demonstrated to facilitate healing of bony defects created by trauma, disease or surgical intervention. Demineralized bone material (DBM) is provided as a dry powder and in various carriers to improve the convenience of handling and wound placement. DBM acts as an osteoconductive scaffold as well as having some osteoinductive properties (ability to induce surrounding patient cells to grow new bone) by virtue of bone morphogenetic proteins (BMP's) retained in the DBM after the demineralization process.
Surgeons have previously used autologous bone, bone marrow and patient blood to provide osteoprogenitor cells to facilitate healing of bony defects. These procedures are highly effective to propagate new bone growth and accelerate wound healing. The use of bone chips and bone marrow taken from the patient's hip (iliac crest) or vertebral intertransverse processes, while providing an effective supply of osteogenic material, creates significant patient morbidity.
As an alternative, bone marrow can be aspirated from the patient, usually from the iliac crest, vertebral body sternum or long bone condyle. This bone marrow aspirate (BMA) contains blood serum, red blood cells and some specific osteoprogenitor cells known as mesenchymal stem cells (MSC) or pluripotential cells. Orthopaedic surgeons have used bone marrow aspirate to facilitate wound healing in spinal fusion, fracture management or other skeletal defects. BMA alone is a slightly viscous, sticky liquid and is difficult to manage for delivery to an operative surgical location. Some workers have mixed BMA with demineralized bone matrix and gotten superior healing rates.
The traditional and current technique involves removing BMA through a bone perforation biopsy-type device and collecting the BMA in a sterile syringe. The BMA is then discharged from the syringe into a container in the operating room. The DBM is then added to the BMA and manually mixed. DBM is provided in a sterile, freeze-dried granular form and delivered from a container, usually a glass bottle.
This manual procedure makes it difficult to control the mix ratio. It may also compromise sterility, as the mixing is being done in the open in the operating room. Once mixed, the formulation may be held for a time ranging from a few minutes to up to an hour and risk drying out and becoming even more difficult to manipulate in the defect area. Finally, the delivery from the mixing container is usually done with a spatula, which results in waste, namely, material being left behind in the container and a loss of the precious bone and marrow cells. Vigorous mixing may also damage the cells in the marrow. The present invention thus overcomes these procedures which are difficult to implement: namely; time constraints, loss of sterility, preservation of cell viability and eliminate waste of material.
The prior art has attempted to solve the problems which occur in mixing bone marrow with a scaffolding material. Isolated marrow cells from quail, in solution, were implanted or delivered via soaking in blocks of calcium phosphate ceramics, the soaked blocks being deposited in subcutaneous sites in a nude mouse. The osteogenesis is a biphasic phenomena in which donor cells are largely responsible for osteogenesis in the first three to four weeks and in the second phase, eight to twelve weeks post surgery the host cells actions predominate and begin to show the formation of marrow of host origin. “The Origin of Bone Formed in Composite Grafts of Porous Calcium Phosphate Ceramic Loaded with Marrow Cells”, by J. Goshima et al., Clinical Orthopaedics and Related Research, vol. 269, pp. 275–283 (1991) Also of interest in this reference is the discussion of prior art on page 281, col. 1.
The use of a bone marrow cells in a bone graft is shown in several U.S. patents, namely, U.S. Pat. No. 5,824,084, issued Oct. 20, 1998 and U.S. Pat. No. 6,049,026 issued Apr. 11, 2000. These patents are directed toward a method for preparing a composite bone graft which includes providing a bone marrow aspirate suspension and passing the bone marrow aspirate suspension through a porous, biocompatible, implantable substrate, such as coralline hydroxyapatite, mineralized or demineralized cancerous bone sections, granules of demineralized bone, sintered cortical or cancerous bone and granular ceramics, to provide a composite bone graft having an enriched population of connective tissue progenitor cells. Because the method is preferably performed intraoperatively it reduces the number of occasions the graftee must undergo invasive procedures. The composite graft includes an enriched population of connective tissue progenitor cells and a greater number of connective tissue progenitor cells per unit volume than that found in the original bone marrow aspirate.
It is also known in the art to use a piston ram carried in a trigger activated gun type device to dispense material carried a cartridge which is loaded into the gun type device. A representative patent showing this type of dispenser is shown in U.S. Pat. No. 4,826,053 issued May 2, 1989.